This invention generally relates to braze alloy compositions. More specifically, the invention relates to nickel-based and cobalt-based braze alloy compositions.
In order to function effectively in a high-temperature environment, heavy alloy components are typically added to strengthen a superalloy. This may result in difficulties for welding joining/repair of superalloy components used in an extreme environment, such as a hot-gas-path airfoil in a gas turbine. Brazing is becoming a more preferred choice for joining/repair of superalloy components as a result of its reduced cost and cycle time. However, it can be challenging to make the braze joints/repair to have certain properties—especially ductility—approaching that of the superalloy substrate material. Generally, a primary obstacle can be the formation of brittle phases in the brazed joint.
Boron has been used extensively in brazing alloys, but brittle borides typically result in poor mechanical properties of the braze joint. A process to improve the mechanical integrity of the braze joint/repaired area generally requires the use of a prolonged diffusion cycle. This approach may reduce the amount of brittle boride phases by homogenization with substrate superalloys or braze powder mixture. This process, however, may require a prolonged cycle time, increasing cost and subjecting the substrate superalloy to thermal degradation.
Braze alloy compositions—and related processes and articles—are described in U.S. Pat. No. 4,414,178 to Smith et al.; U.S. Pat. No. 5,240,491 to Budinger at al.; U.S. Pat. No. 5,735,448 to Draghi et al.; U.S. Pat. No. 5,783,318 to Biondo et al.; U.S. Pat. No. 6,503,349 to Pietruska et al.; U.S. Pat. No. 6,520,401 to Miglietti; U.S. Pat. No. 6,530,971 to Cohen et al.; U.S. Pat. No. 6,165,290 to Rabinkin; and U.S. Patent App. Pub. No. 20050067061 to Huang et al. Where hafnium is present in a low-weight percentage, it generally acts as a grain boundary strengthener—not as a reducer of the braze alloy composition's melting point.